Clinical data and the common embryological origin of the pigment epithelium of the iris and retinal pigment epithelium suggest that the latter may be involved in the pigment dispersion syndrome (PDS). In our study functional changes of the retinal pigment epithelium were evaluated by electro-oculography in 10 PDS patients, 10 patients with chronic open-angle glaucoma (COAG) and 10 normal subjects. The mean dark-trough latency and Arden ratio for the PDS group were significantly lower than those of the COAG and control groups. Analysis of the Arden ratios based on the Kruskall-Wallis test revealed that 30% of the PDS values were subnormal with respect to the control group mean -1 SD. These results indicate primary involvement of the retinal pigment epithelium in PDS.